Fixed read tag to throw exception on file error unstead of looping forever.

__read.cpp

@@ -14,6 +14,8 @@ namespace jet {
       if(hasContainer)
 	throw coreutils::Exception("read tag does not have a container.");
       fd = open(variables["file"].c_str(), O_RDONLY);
+      if(fd < 0)
+	throw coreutils::Exception("file name is not found.");
       global.variables[variables["name"]].read(fd);
       close(fd);      
    }